1. In this paper the author studied on the host-parasite interaction between Lepidopterous egg paprasites and their hosts in the rice field.2. Surveys were done in the rice fields at four different places in Matsue Vity, in 1955 and 1956. A list of Lepidopterous species whose eggs were collected and species of egg parasites emerged from them, and the host-parasite relationships betweem them as follows :<tt> Egg parasite Host species ┌ Chilo suppressalis WALKER │ Susumia exigua BUTLER (?) │ Naranga aenescens MOORE │ Cirphis unipuncta HAWORTH Trichogramma japonicuum ASHMEAD │ Sesamia inferens WALKER (?) │ Parnara guttata BREMER et GREY │ Pelopidas mathias oberthuri EVANS └ Polytremis pellucida MURRAY (?) ┌ C. suppressalis WALKER T. chilonis ISHII │ └ N. aenescens MOORE Phanurus beneficiens ZEHNTER C. suppressalis WALKER Phanurus sp. N. aenescens MOORE ┌ P. guttata BREMER et GREY Telenomus sp. │ P. mathias oberthuri EVANS └ P. pellucida MURRAY (?)</tt>Of these, C. suppressalis and N. aenesens as host, and T. japonicum and P. beneficiens as parasite seems to be most important in an eco-system of these relationships.3. In spite of the existence of host eggs, neither T. japonicum nor P. beneficiens were found in the rice field before the end of May. 4. At the end of the emergence period of C. suppressalis of its first brood, high percentage of the egg masses was parasitised, in general, by T. japonicum, accompanying with high percentage of parasitism of eggs in an egg mass, in which the most parts of the eggs were superparasitised.5. In the rice field, P. benrficiens were common from the end of May to the middle of June, and then became rare regardless of the existence of egg of C. suppressalis of the first brood, but it reappeared in the egg masses of C. suppressalis of its second brood. 6. It is thought that the rice green caterpillar, Naranga aenescens, was actually only host which was maintainnig the population of T.japonicum during the periods of the absence of egg of C. suppressalis.7. The emergences of T. japonicum were recorded from the egg masses of an unknown species collected in the rice field in the early summer of 1956. The egg was thought to belong to Order Diptra.